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8.3 Benefit-Cost Results Figure 8.4 shows the original benefit-cost results from the I-5 CSMP (Caltrans 2012). The CSMP benefit-cost analysis includes all of the CSMP scenarios shown earlier in Figure 3.8, with the exception of the enhanced incident management scenarios. These scenarios were excluded from the benefit-cost analysis in the CSMP, so the study team decided not to include them in the test to include C11 reliability benefits. Figure 8.4. Benefit-cost results in CSMP for I-5 facility. Source: Caltrans, I-5 CSMP. The benefit-cost calculations shown in Figure 8.3 include three types of user benefits: travel time (or delay) savings, vehicle operating cost savings, and emission savings. These benefits were estimated using results from microsimulation runs. As can be seen in Figure 8.4, the CSMP benefit-cost analysis includes scenarios with costs ranging from $40 million for advanced ramp and connector metering to $1,052 million for additional general-purpose and high-occupancy vehicle lanes along the facility. The CSMP assumes sequential implementation starting with the interchange and ramp improvements found in Scenarios 1 and 2. The benefit- cost ratios range from 0.7 for the interchange and ramp improvements to 15.2 for low-cost ramp and connector metering. Figure 8.5 shows the original benefit-cost results from the I-210 CSMP (SCAG and Caltrans 2010). As can be seen in the exhibit, significantly more strategies were tested on the I- 180
210 facility. These strategies resulted in abnormally high benefit-cost ratios due to heavy congestion on the facility and relatively low costs for improvements (ranging from $4.0 million for ramp closures to $44.0 million for auxiliary lanes and ramp improvements). The exhibit does not show two scenarios from the original CSMP benefit-cost and analysis, Scenarios 13 (interchange modification) and 14 (drop ramp and widening), which have benefit-cost ratios of 1.4 and 6.1, respectively. These scenarios included improvements on portions of the facility outside the area modeled in the C11 tool, so the scenarios were not included in the reliability test. Figure 8.5. Benefit-cost results in CSMP for I-210 facility. Source: SCAG and Caltrans, I-210 CSMP. For both facilities, the study team estimated travel time reliability benefits using the C11 tool and added these benefits to the results shown in Figures 8.4 and 8.5. In the process of adding these benefits, the study team discovered that the C11 tool does not take into account the average vehicle occupancy (AVO) for automobiles. As a result, the value of time for personal travel should been multiplied by the AVO prior to running the C11 tool. The study team decided to adjust the mobility (recurring delay) and reliability (unreliability) benefits as part of the interpolation spreadsheet. Figure 8.6 shows the benefit-cost ratios that resulted from including the reliability benefits estimated in the C11 tool for the I-5 facility. The shaded portion of the bar indicates benefits due to improvements in travel time reliability, while the solid portion indicates the 181
benefits in the original benefit-cost analysis. Comparing Figure 8.6 with Figure 8.4 demonstrates that the addition of reliability benefits does not affect the rank order of the projects by their total benefit or their benefit-cost ratios. However, the addition of reliability benefits boosts the total benefits for the interchange and ramp improvements in Scenarios 1 and 2 so that the total benefit-cost ratio exceeds one. This suggests that ignoring travel time reliability benefits could make a cost-beneficial operational project be not cost-effective. Figure 8.6. Benefit-cost results for I-5 facility with C11 reliability estimate added. Figure 8.7 shows the result of adding the C11 reliability estimates to the benefit-cost analysis for the I-210 facility. Again, the shaded portion of the bars shows the addition of the reliability benefits. The impact is similar to that found on the I-5 facility. Adding travel time reliability does not reorder the projects in terms of total benefits or benefit-cost ratios. The advanced ramp metering project found in Scenarios 3 and 4 receives the greatest benefit from the inclusion of travel time reliability. The reliability impact on auxiliary lanes and ramp improvements is much larger in Scenarios 9 and 10 than in Scenarios 3 and 4. However, the magnitude of this change is related to the size of the overall benefits. Original Benefits from CSMP Modified Reliability Benefits Scenario Project Cost 182
Figure 8.7. Benefit-cost results for I-210 facility with C11 reliability estimate added. However, it may not make sense to simply add the C11 reliability benefits to the original CSMP benefit-cost analysis. As shown in Figures 8.8 and 8.9, the C11 Reliability Analysis Tool did not estimate the same mobility (recurring delay) benefits as did the CSMP microsimulation analysis. In most cases, the C11 tool underestimates mobility benefits compared to the CSMPs. Original Benefits from CSMP Modified Reliability Benefits Scenario Project Cost 183
Figure 8.8. I-5 Recurring delay benefit from C11 tool compared with mobility benefit in CSMP. Figure 8.9. I-210 recurring delay benefit from C11 tool compared with mobility benefit in CSMP. The CSMP benefit estimates are probably more accurate because they are based on microsimulation modeling rather than a sketch planning tool. The microsimulation modeling does a better job of capturing the impact of bottleneck relief on the operational performance of the facility. The discrepancy in the recurring delay estimates could also be due to the capacity 184
improvement assumption used to model some scenarios in the C11 tool. For the I-210 facility, another factor is that the CSMP covered a slightly larger area than was modeled in the C11 tool. The study team decided to adjust the C11 tool results by assuming that the microsimulation model is more accurate in modeling mobility benefits, but that the C11 tool is accurate in estimating reliability benefits relative to mobility benefits. The second assumption is based on the C11 tool using volume-to-capacity (v/c) ratios to estimate both mobility and reliability benefits. In fact, the C11 tool results suggest that reliability benefits are typically about 30 percent of the mobility benefits. This ratio ranges from 30 to 32 percent for the I-5 facility and from 29 to 36 percent for the I-210 facility. Figures 8.10 and 8.11 show the benefit-cost results after the C11 tool outputs are adjusted to match the microsimulation results (and maintain the reliability to mobility ratio). As with the unadjusted figures, the inclusion of the reliability benefits does not impact the rank order of the improvements for either facility in terms of total benefits or benefit-cost ratios. Two differences are worth noting. First, the benefit-cost ratio of I-5 Scenarios 1 and 2 is below one, so the inclusion of travel time reliability does not make the project cost beneficial. A project closer to breaking even might have benefitted from the inclusion of travel time reliability. Second, I-5 Scenarios 3 and 4 have nearly the same total benefits as I-210 Scenarios 9 and 10, while the benefits of the I-210 scenarios were higher without reliability. Clearly, travel time reliability can make a difference in the ranking of projects that have very similar benefits. 185
Figure 8.10. Benefit-cost results for I-5 facility with C11 reliability estimate modified. Original Benefits from CSMP Modified Reliability Benefits Scenario Project Cost 186
